132 HP at 4200 RPM means you have 165 lb/ft of torque at 4200 RPM. So your torque is dropping off not far over your peak RPM, and is below 200 by 3500 RPM.

Theoretically, you should run from about 80% of peak torque to the HP peak. That doesn't look to practical in your case. How does it feel if you keep it between 2000 and 3000 RPM?

What gears can you easily get for your axle?

You can plug numbers in here to get a better idea for yourself.

https://spicerparts.com/calculators/...que-calculator

There are lots of ways to skin the cat here. Gears, beef up you motor, replace with a 292, Coyote swap. Whatever you can stand.

 

Those published numbers are peaks, right? I used the torque/hp calculator link, but I can really only get hp at the specified torque (215) from 1800 to 2200 rpm, and the torque value at the specified hp (132@4200). I need to know 2 of those variables in order to calculate either one throughout the range of RPM, unless I'm missing something.

What I did do, though, is used the Spicer RPM-from-gear-ratio calculator (https://spicerparts.com/calculators/...rpm-calculator), and made of table of vehicle speeds (using my tire diameter) for the available differential gear ratios available for the Spicer/Dana 44 rear end: 3.92 (my current), 3.73, 3.54, and 3.31. The table is above.

I plugged in the values according to the shop manual, then filled the table in with vehicle speeds at the listed RPM values for each of the 4 gear ratios. As you can see, I filled in the table for the RPM that produced around 75mph (@3400rpm) for the lowest ratio (3.92).

I'm not sure I understand your reply entirely, where you stated that I should "run from about 80% of peak torque to the HP peak." If the values given in the shop manual are peak values, then 80% of peak torque would be 172, so are you saying that the engine needs to be 172 minimum throughout that range of 2300-4200 rpm, correct?. There doesn't appear to be a way to calculate the torque at 3400 rpm without knowing the horsepower at that same point, using the formula: τ=hp*5252/RPM, and linear interpolation of the given peak values is definitely out, for a couple different reasons.

Is there a way to identify the rpm value at which the torque drops below 172? So, if the torque remains above 172 until 3400 rpm, I would be good-to-go at ANY of those gear ratios... right? The key seems to be how to calculate the torque at 3400 rpm without knowing the hp.

Am I way off track, here?

 

We know peak torque rpm is 1800 to 2200, so we can plug that in and get the HP number there. (90 at 2200 rpm)

We know peak HP is 132 at 4200 rpm, and via calculation or calculator, we know that means 165 ft/lb at 4200 rpm.

Since those are the peaks, we know that you can't use a HP number higher than 132 anywhere, nor can you use a torque number of more than 215 anywhere.

So if you plug in 131 HP at a particular RPM, you can see what the maximum torque for that rpm would be, and if it shows greater than 215 you have to reduce the rpm number. It's an estimation and projection based on known numbers. It's not exact, but if you were to graph the slide from 215 to 165 between 2200 rpm and 4200 rpm, and add the slide up from you would see how the torque slides down the scale as the hp creeps up from 90 at 2200 rpm to 132 at 4200.

80% of peak torque rpm was said to be the most efficient speed to run an engine for cruise.
(page 23 regarding volumetric efficiency, eye glazing details: https://books.google.com/books?id=DwUMAaiyMoYC&pg=PA23&lpg=PA23&dq=80%25+of +maximum+torque&source=bl&ots=04Tr5doNvC&sig=sCAUy fgRyxuYvPWHn2aFQSRwpFY&hl=en&sa=X&ved=2ahUKEwj0pcm t-vzcAhUW0IMKHRWjBaE4ChDoATAEegQIBhAB#v=onepage&q=80 %25%20of%20maximum%20torque&f=false

Anyway, using the hocus pocus method above, it appears you hold 200 lb/ft until just over 3000 rpm, thus the "how does it feel between 2000 & 3000 rpm?"

Given the loads here, I wouldn't want to run it too much below 2000 unless it felt smooth and happy. By that I mean smooth and it still has good throttle response, I.e. not lugging.

Given the way a y block is built, I don't think you need to worry about much with a redline of 4500. But I doubt it would be happy there. The key is to find the happy spot--no lugging, no vibration, good throttle response, at the lowest rpm.

 

The yblocks can take higher rpms, I have learned. My 54 has the stock 3.92 rear end. I can run it at 60 mph with no problems.